This invention relates to circuit breakers and more particularly to a circuit breaker of the kind in which a puffer type circuit breaking unit is housed within a tank of metal material for compressing an arc extinguishing gas and supplying a puff of this compressed gas to the space between the parted contacts as soon as the circuit breaking operation takes place.
The increase in the electric power demand in recent years is quite remarkable, and this is accompanied by a tendency toward a further increase in the capacity of power systems. Circuit breakers are used in a power system as a means for protecting the power system against short-circuit and other troubles. In the event of occurrence of trouble in a section of the power system, the circuit breakers must interrupt immediately the flow of current through the electrical path in order to quickly cut off the faulty section from the remaining sound sections. The current, for example, short-circuit current to be interrupted increases remarkably with the increase in the capacity of the power system. Thus, the contact assembly in the circuit breaking unit in which an arc is produced during the interruption of the short-circuit current tends to be excessively damaged due to the fact that the arc energy is very large. Therefore, the contact assembly must be inspected after the interruption of such a large current or periodically and must be replaced by new parts as required. However, the period of time required for this work must be reduced to a minimum since power supply is interrupted completely during this period of time. This is demanded especially in principal power transmission lines.
In the prior art circuit breakers of this kind, the entire circuit breaking unit is taken out of the tank for the inspection or replacement of the contact assembly. However, the work for taking the circuit breaking unit out of the tank is extremely troublesome. Further, this work is inefficient and time consuming since the entire circuit breaking unit must be taken out of the tank in spite of the fact that the inspection is actually required for the contact assembly only. Further, in the case of circuit brakers having a higher voltage rating and a larger capacity, this work becomes more troublesome and time consuming since it is required to provide impedance elements such as making resistors or voltage dividing capacitors in electrically parallel relation with the circuit breaking unit.